1. Field of the Invention
This invention relates to permselective membranes and their preparation and use, said membranes comprising hydrazide-containing aromatic polymers and metals in valence states which form square planar coordination complex structures with ligands. These membranes are particularly useful for the reverse osmosis desalination of sea and brackish saline waters.
2. Description of the Prior Art
Permselective membranes which preferentially permeate certain components of liquid mixtures while retaining other components have long been known, as has the principle of reverse osmosis, wherein a hydrostatic pressure in excess of the equilibrium osmotic pressure of a liquid mixture is applied to the mixture to force the more permeable components of the mixture, usually water, through the membrane in preference to the less permeable components, usually a salt, contrary to normal osmotic flow.
It is well known that complete separation of the more permeable from the less permeable components of liquid mixtures is never obtained with permselective membranes in practical use. All components of a mixture permeate to some degree through any membrane which has a practical permeation flux rate for the more permeable components. In general, membranes of any particular type can be prepared with a range of flux rates, the membranes having higher flux rates also have correspondingly lower rejection efficiencies for the less permeable components. A principal goal with such membranes has been the production of membranes with economically attractive optimum balances of high flux rates for more permeable components and high rejection efficiencies for less permeable components of liquid mixtures.
U.S. Pat. No. 3,567,632 discloses asymmetric permselective membranes made from substantially linear synthetic organic nitrogen-linked aromatic polymers, including polymers containing amide and diacyl hydrazide linking groups. This reference does not disclose such membranes containing complexed metals.
U.S. Pat. No. 3,526,001 discloses that permselective membranes made of a variety of polymers can be used to separate cupric salts from aqueous solutions by a reverse osmosis process. This reverse osmosis process will not form a membrane containing a copper complex.
Frazer and Wallenberger described in the Journal of Polymer Science, Part A, Volume 2, pages 1825-1832 (1964) the preparation and properties of metal chelates of aromatic polyhydrazides. The chelate-containing films were prepared by soaking films of polyhydrazides, i.e. poly(diacyl hydrazides), presumably formed by substantially complete evaporation of solvent from a pellicle of a polymer solution, in solutions containing Cu(II) and Co(II) salts in undefined solvents. The resulting films are not permselective. The reference also teaches mixing a polymer solution with a salt solution in a polymer solvent and producing bulk chelates that are intractable.
Furthermore, this reference teaches chelates of polyhydrazides with metal ions such as Hg(II), Pb(II), and Al(III) which do not form square planar coordination complexes with ligands. Attempts to incorporate such metal ions into membranes of the polymers useful in the membranes of this invention have resulted in no significant changes in the measured permselective separation properties of the membranes.